1. Field of the Invention
The present invention relates to an image-forming machine of the type of electrostatic photography, such as a laser printer, a copier or a facsimile and, particularly, to an image-forming machine of the type of electrostatic photography equipped with a protection cover capable of opening and closing the exposing surface of a photosensitive material drum.
2. Description of the Related Art
In an image-forming machine, in general, a drum unit that includes a photosensitive material drum or a process unit that includes the drum unit and a developer, is equipped with a protection cover for opening and closing the exposing surface of the photosensitive material drum. JP-A-2004-151568 is disclosing an image-forming machine in which the drum unit in the process unit is equipped with a protection cover. In this machine, the drum unit includes an arm member that is rotatably arranged to open and close the protection cover, and a torsion coil spring provided between the drum unit and the arm portion so as to urge the arm member at all times toward the closed position where the protection cover conceals the exposing surface of the photosensitive material drum. When the process unit is mounted on the machine body, the arm member interferes with a stationary portion of the machine body and is rotated against the spring force of the torsion coil spring, causing the protection cover to open so that the exposing surface is exposed. When the process unit is removed from the machine body, on the other hand, the arm member is liberated from the interference with the stationary portion of the machine body, and is rotated up to the closed position due to the spring force of the torsion coil spring, causing the exposing surface to be concealed.
If the jamming occurs while the image-forming machine is in operation, the process unit is removed from the machine body to remove the jamming. After the jamming has been removed, the process unit is mounted on the machine body. The process unit is also removed and is, then, mounted at the time of regular maintenance. The protection cover temporarily coneals the exposing surface of the photosensitive material drum at the time of the above removal and mounting in order to protect the surface from being damaged.
When the drum unit or the process unit is to be replaced in the image-forming machine in which the protection cover is provided for the process unit including the drum unit or in the image-forming machine in which the protection cover is provided for the drum unit that is independently and detachably attached to the machine body, it is forced to exchange the protection cover and the related members together with the drum unit or the process unit though they really do not have to be renewed, accounting for the waste of materials and driving up the cost. Besides, the disposal of parts in an increased amount is not desirable even from the standpoint of protecting the environment.